There have been further developments for LTE, for instance relating to a Beyond 4G (B4G) radio system which is assumed to be commercially available in 2020. It might however also be introduced in an evolution of LTE at any date within any new release.
LTE provides a peak bit rate of 30 bps/Hz by using 64QAM modulation and 8×8 MIMO transmission. As a result, B4G may require a higher order modulation, for instance 256QAM, than 64QAM in order to meet future requirements. Higher order modulations may be relevant for example in relay backhaul due to better channel quality and better radio frequency (RF) properties which are more easily feasible for relays than for user equipments (UEs) or for isolated indoor cells where the UEs are close by and therefore both having a good link to the access point and no or very little interference from other access points due to attenuation by the walls.
The modulation order determination of LTE Release 10 is described in TS 36.213 V10.3, chapter 7.1.7 and CQI definition in chapter 7.2.3. In LTE (and LTE-Advanced), theoretical spectral efficiency is restricted by 64QAM modulation. An improved spectral efficiency may be gained with extension to 256QAM.
In the LTE standard, there is defined a MCS (modulation and coding scheme) index and modulation table and CQI (channel quality indicator) table. These are used for determining and selecting appropriate modulation and coding schemes. The current tables support up to 64QAM. The problem is how to introduce a 256QAM extension or any other higher order modulation extension for LTE while maintaining backward compatibility and avoiding too much complexity.
There may be a need for an improved and flexible system and method being adapted to allow an extension to a higher order modulation while remaining backward compatible for LTE. In particular it is desirable to maintain signaling formats in particular utilize the same number of bits as otherwise different encoding schemes need to be used and potentially so called blind decoding has to be applied.